1. Field of the Invention
This invention relates generally to the fabrication of merged magnetic read/write heads and slider assemblies and, more particularly, to the fabrication of such a head and slider assembly with improved heat spreading and dissipation characteristics to eliminate problems associated with thermal expansion and protrusion of head elements during operation.
2. Description of the Related Art
A merged magnetic read/write head and slider assembly consists essentially of a magnetoresistive read sensor element formed on the pole pieces of an inductively magnetized write element and mounted within, or fabricated as an integral part of, a slider assembly that physically and electrically connects the head to an actuator arm. The read/write head is subjected to complex thermal stresses during its normal operation due to the buildup of thermal energy from Joule heating in its read and write stages (sensing current in the read element and write current in the write coil). The heat dissipation properties of the read/write head are limited by the thermal conductivity of the protective overcoat material (typically sputtered alumina) that covers the head. Since alumina is a relatively poor conductor of heat, a temperature buildup occurs in both the head and the overcoat as the overcoat is unable to eliminate the heat produced in the head with sufficient rapidity.
FIGS. 1 and 2 show two schematic views of a read/write head and slider assembly. FIG. 1 shows a cross-section of the head attached at (15) to the actuator arm (30). Details include the overcoat (2), the upper (6) and lower (4) pole-pieces and the insulation imbedded coil structure (5) that inductively activates them. The read element (8) is generally formed beneath the lower pole piece (4) which then also serves as an upper shield for the read head. The air-bearing surface of the head, at which the read element is positioned, is indicated as (1) and the dimensional direction “x” is also shown. The trailing end, containing the connecting pads (only (10) is shown), is indicated as (14). FIG. 2 is a schematic drawing showing the trailing end surface (14) of the read/write head assembly where it attaches to external wiring (shown as (13) in FIG. 1) along the actuator arm. The dimension “z” on the drawing would be coming out of the plane of the drawing in FIG. 1. FIG. 2 also shows four gold pads (16, 18, 20, 10) which make the electrical connections to the head assembly. Two of the pads (10 & 20) provide the sense current for the read sensor through internal wiring (9), while the remaining pads (18, 16) provide the coil current for the write head through wires (19). These figures will also be discussed below in the context of the description of the preferred embodiment.
Seagle (U.S. Pat. No. 5,936,811) provides a slider assembly similar to that in FIGS. 1 & 2 in which the current carrying leads are disposed in a manner that eliminates the need for vias passing through the insulating layers and shield layers to allow the electrical activation of the read and write sensors.
Chang et al. (U.S. Pat. No. 6,158,107) provide a merged read/write head in which the pole tips of the write head are more advantageously defined by use of a self-alignment formation process and show the use of a substantial overcoat in the head formation.
Maries et al. (U.S. Pat. No. 3,770,403) discloses a magnetic head assembly in which the read/write circuit portions of the assembly are formed on a chip and bonded to head assembly by a glass-ceramic material whose coefficient of expansion matches the coefficient of expansion of the parts to be joined. Another feature of this structure is that the method of mounting the head assembly on the support arm allows the air flow past the assembly to act as a coolant for the circuit chip and also allows the thermal conductivity of the metal structure of the arm to act as a heat sink for the circuit chip.
Phipps et al. (U.S. Pat. No. 5,757,590) deals with the problem of electrostatic charge buildup on read/write heads, which is another problem associated with rapid relative movement between the head and the recording medium. Phipps provides a fusible link element connected across the existing terminal pads of the head to discharge the unwanted buildup.
Wang et al. (U.S. Pat. No. 6,130,863) show the use of a magnetic coil and slider assembly even in the field of magneto-optical storage systems.
Han et al. (U.S. Pat. No. 6,103,136) shows a magnetoresistive read head that typifies those found in the merged read/write heads referred to in the present invention.
None of the prior art cited deals with the significant problem of heat buildup in head elements such as write coils, magnetic pole pieces, overcoat regions and magnetoresistive sensing formations. This heat buildup is not only damaging to the performance of the elements, but differential thermal expansion causes protrusion of elements relative to each other and relative to the air bearing surface, which protrusion can cause damage to the rapidly moving storage medium. It is, therefore, the purpose of the present invention to provide a simple and efficient method whereby the heat dissipation properties of a read/write element can be significantly improved.